Wheelsets for railroad cars are usually comprised of an axle and two wheels. The wheels are pressed on to the axle shaft and are rigidly mounted so that both wheels turn exactly the same degree of rotation during operation. The wheelset assembly may be supported by journal bearings outboard of each wheel or the bearings may be located inboard of the wheels. The rigid assembly of the wheels on the axle and the lack of independent rotation of the wheels is the cause of slippage on the rail when the wheelset operates in curved sections of track. This slippage causes wear on the wheel treads and rails and is a prime cause of corrective maintenance on both the wheels and the track.
Efforts have been made to overcome the problems associated with the rigid assembly of conventional wheelsets by placing bearings between the axle and the wheel on at least one end of the axle to permit differential speeds of rotation of the wheels at opposite ends of the axle. In such cases, a hub is located on at least one end of the axle and a wheel is mounted on the hub or on the axle and its rotation with respect to the axle is facilitated by a bearing assembly. As discussed hereafter, electrical continuity from the two rails through the wheels and the axle is necessary for operation of signal devices or the like. This electrical continuity was established with the conventional railroad wheelsets wherein the wheels were rigidly fixed through opposite ends of the axle. However, with the advent of one of the wheels being mounted on the axle by means of a bearing assembly, the electrical continuity between the wheels was less than perfect. With the advent of non-metallic bearings, the electrical continuity was not possible.
A typical signal device for a road crossing, for example which utilizes a crossing arm, flashing lights, and the like, derives electrical energy from any conventional source. A low voltage is imposed on a given dedicated length of rail on opposite sides of the signal, with the opposite rail being electrically connected to the signal whereupon the signal circuit is closed when the wheel assembly of a train initially moves onto the dedicated length of rail. The circuit is completed between the opposite rails through the wheels and axle of the train""s wheel assemblies which allow the flow of energy therethrough to electrically connect the opposite rails.
Even when a differential action wheelset is used, an adverse situation may arise wherein, upon beginning motion, one of the independent wheels moves in one direction and the other wheel on the axle moves in the opposite direction in a pivoting effect. That is because when an axle is provided with one or more independently rotatable wheels, it is possible for the axle to rotate about its vertical centerline if one of the wheels rotates in one direction and the other wheel rotates in the opposite direction. If the axle with the independently rotatable wheels is mounted in a short wheelbase two-axle truck, it may be possible for the two wheels on one side of the truck to move in one direction, while the two wheels on the other side of the truck rotate in the opposite direction. This action may result in derailing the truck and will be more pronounced and prevalent in a short wheelbase two-axle truck than in a long wheelbase two-axle truck.
Field testing by the American Association of Railroads (described in ASME Paper No. 7-5, dated Sep. 12-15, 1988) indicates that in certain situations it is desirable to have the wheelset in the leading axle position of a multi-axle truck be equipped with non-independent wheel rotation, and the wheelset in the trailing axle position equipped with independently rotating wheels. The problem in such an arrangement is that the leading axle wheelset when the railroad car is operating in one direction is the trailing axle wheelset when the railroad car operates in the opposite direction.
It is, therefore, a principal object of this invention to provide a railroad car wheelset with independently rotating wheels in which the differential action is made inoperable upon stopping and at lower speeds, and when the differential action is automatically resumed when the wheel rotation reaches a predetermined operational speed.
A further object of this invention to provide a railroad wheelset with independent rotation of wheels with respect to each other which will consistently retain the electrical continuity between the opposite wheels and the rails upon which they are supported.
A still further object of this invention is to provide a wheelset with independent rotation of the wheels with respect to each other which can be used in existing truck designs without modification to the truck structures or the braking system.
A still further object of this invention is to provide a railroad wheelset which requires no additional maintenance than conventional rigid wheelsets after installation and during service.
A still further object of this invention is to provide a railroad wheelset with independently rotating wheels in which the differential action is made available with no decrease in safety or reliability.
A still further object of this invention is to provide a railroad car wheelset with independent wheel rotation which can be economically manufactured and applied to railroad cars of all types.
A still further object of this invention is to provide a railroad car wheelset in which both wheels can rotate independently in one direction on the axle, and be locked against rotation in the other direction.
A still further object of this invention is to provide the alternate capability of operating a wheelset either as a fixed-wheel wheelset in one direction and as an independently rotatable wheel wheelset in the opposite direction.
A still further object of this invention is to permit the alternate capability to be achieved using a minimum of special parts and a maximum of common parts.
These and other objects will be apparent to those skilled in the art.
The railroad car wheelset of the present invention includes an axle with one wheel rigidly attached as in conventional railroad practice. This wheel is permitted to rotate by means of journal bearings either on the extreme ends of the axle or inboard of each wheel location. At the location of the other wheel, the axle is provided with a smooth surface and a self-lubricating bearing is provided. The axle shaft is provided with a boss or other means of preventing the independently rotating wheel from migrating laterally out of proper alignment. A self-lubricating thrust bearing is located between this boss and the side of the wheel to eliminate any possible galling between the two moving surfaces. A removable retainer plate is located on the other side of the independently rotating wheel to prevent the wheel from moving laterally in that direction. Adjacent the removable retainer plate is an electrical contactor which can conduct an electrical current from the wheel to the axle shaft, to permit the wheelset to properly operate railway signals or other systems dependent on electrical continuity. In lieu of the self-lubricated bearings, the bearings can be comprised of a lubricant coating permanently bonded to the bearing surface of the hub adjacent the independently rotatable wheel.
An axle with two wheels in which one wheel may rotate independently of the other may be pivoted about its vertical centerline in the event one of the wheels rotates in one direction and the other wheels rotate in the opposite direction. The railroad car wheelset of the present invention may include a means of locking the independently rotatable wheel to the axle rigidly when the rotation of the wheel ceases, or when the wheel is rotated slowly. This locking means automatically releases when the wheel and axle reach a predetermined speed of rotation, at which time the differential action of the independently rotating wheel is again permitted.
An alternate form of the present invention is provided for situations in which one of the wheelsets in a truck is desired to be of the fixed-wheel type in one direction and also is desired to function as an independently rotatable wheel wheelset in the opposite direction. The railroad car wheelset of the present invention includes a means of locking the independently rotatable wheel to the axle rigidly when the rotation of the wheel is in one direction, and automatically unlocking the independently rotatable wheel from the axle when the rotation of the wheel is in the opposite direction. The proper arrangement of these wheelsets in the truck frame permits the leading axle to automatically operate as a fixed-wheel wheelset and the trailing axle to operate as an independently rotatable wheel wheelset regardless of which direction the railcar is moving.
Thus, the independently rotatable wheel is locked to the axle automatically in one direction and permits the independent rotation of the wheel automatically when the rotation is in the opposite direction. By arranging the wheelsets 180xc2x0 from each other in the truck frame (as shown in FIG. 14), the trailing axle is always equipped with independently rotating wheels and the leading axle is always functioning as a conventional axle with two fixed and non-independently rotating wheels.
The hubs are either integral with the axle, or pressed on the axle. An alternate form of the invention is provided in which both wheels can rotate independently on the axle in one direction, and be restrained from rotating independently in the opposite direction.